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The refractive index of the material of a concave lens is $μ$ . It is immersed in a medium of refractive index $μ_{1}$ . A parallel beam of light is incident on the lens. The path of the emergent rays when $μ_{1} > μ$ is :

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Important Questions on Ray Optics and Optical Instruments

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A thin convex lens of focal length

f

is put on a plane mirror as shown in the figure. When an object is kept at a distance

a

from the lens-mirror combination, its image is formed at a distance

\frac{a}{3}

in front of the combination. The value of

a

is:

EASY

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

For a thin lens of focal length

f

, if the object and image distances from the optical centre are

u

and

v

, then which of the following is the correct lens formula? (Assume standard sign-convention)

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A convex lens of focal length

f

is placed some where in between an object and a screen. The distance between object and screen is

x

. If numerical value of magnification produced by lens is

m

, focal length of lens is

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A diverging lens with magnitude of focal length

25 cm

is placed at a distance of

15 cm

from a converging lens of magnitude of focal length

20 cm

. A beam of parallel light falls on the diverging lens. The final image formed is:

EASY

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A plano-convex lens of refractive index

μ_{1}

and focal length

f_{1}

is kept in contact with another plano-concave lens of refractive index

μ_{2}

and focal length

f_{2} .

If the radius of curvature of their spherical faces is

R

each and

f_{1} = 2 f_{2},

the

μ_{1}

and

μ_{2}

are related as:

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

Two identical glass

(μ_{g} = \frac{3}{2})

equiconvex lenses of focal length,

f

are kept in contact. The space between the two lenses is filled with water

(μ_{w} = \frac{4}{3})

. The focal length of the combination is

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

Diameter of a plano - convex lens is

6 cm

and thickness at the centre is

3 mm

. If the speed of light in the material of lens is

2 \times 1 0^{8} m s^{- 1}

, the focal length of the lens is:

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

The image of an object, formed by a plano - convex lens at a distance of

8 m

behind the lens, is real and is one-third the size of the object. The wavelength of light inside the lens is

\frac{2}{3}

times the wavelength in free space. The radius of the curved surface of the lens is

EASY

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

Formation of real image using a biconvex lens is shown below:

Question Image

If the whole set up is immersed in water without disturbing the object and the screen positions, what will one observe on the screen?

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A plano - convex lens (focal length

f_{2}

, refractive index

μ_{2},

radius of curvature R) fits exactly into a plano - concave lens (focal length

f_{1},

refractive index

μ_{1},

radius of curvature R). Their plane surfaces are parallel to each other. Then, the focal length of the combination will be:

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A point source of light is moving at a rate of

2 cm s^{- 1}

towards a thin convex lens of focal length

10 cm

along its optical axis. When the source is

15 cm

away from the lens the image is moving at

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A small object is placed $50 cm$ to the left of thin convex lens of focal length $30 cm$ . A convex spherical mirror of radius of curvature $100 cm$ is placed to the right of the lens at a distance of $50 cm$ . The mirror is tilted such that the axis of the mirror is at an angle $θ = 30 °$ to the axis of the lens, as shown in the figure. If the origin of the coordinate system is taken to be at the centre of the lens, the coordinates (in $cm$ ) of the point $(x, y)$ at which the image is formed are:

Question Image

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

An optical device is constructed by fixing three identical convex lenses of focal lengths

10 cm

each inside a hollow tube at an equal spacing of

30 cm

each. One end of the device is placed

10 cm

away from a point source. How much does the image shift when the device is moved away from the source by another

10 cm ?

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

Two thin lenses have a combined power of

+ 9 D .

When they are separated by a distance of

20 cm,

their equivalent power becomes

+ \frac{27}{5} D,

then their individual powers are

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A concave lens made of material of refractive index

1.6

is immersed in a medium of refractive index

2.0 .

The two surfaces of the concave lens have the same radius of curvature

0.2 m .

The lens will behave as a

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A point object is placed

20 cm

left of a convex lens of focal length,

f = 5 cm

(see the figure). The lens is made to oscillate with a small amplitude

A

along the horizontal axis. The image of the object will also oscillate along the axis with
Question Image

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

The word KVPY is written on $a$ board and viewed through different lenses such that board is at a distance beyond the focal length of the lens.

Question Image

Ignoring magnification effects, consider the following statements.
$(I)$ First image has been viewed from the planar side of a plano-concave lens and second image from the planar side of a plano-convex lens.
$(II)$ First image has been viewed from the concave side of a plano-concave lens and second image from the convex side of a plano-convex lens.
$(III)$ First image has been viewed from the concave side of a plano-concave lens and second image from the planar side of a plano-convex lens.
$(IV)$ First image has been viewed from the planar side of a plano-concave lens and second image from the convex side of a plano-convexlens.

Which of the above statements are correct?

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

What is the position and nature of image formed by lens combination shown in figure? (

f_{1}, f_{2}

are focal lengths)

Question Image

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

The eye can be regarded as a single refracting surface. The radius of curvature of this surface is equal to that of the cornea

(7 .8 mm)

. This surface separates two media of refractive indices

1

and

1.34

. Calculate the distance from the refracting surface at which a parallel beam of light will come to focus.

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A convex lens is put

10 c m

from a light source and it makes a sharp image on a screen, kept

10 c m

from the lens. Now a glass block (refractive index 1.5) of

1.5 c m

thickness is placed in between the light source and the lens. To get the sharp image again, the screen is shifted by a distance

d .

Then

d

is:

The refractive index of the material of a concave lens is μ . It is immersed in a medium of refractive index μ 1 . A parallel beam of light is incident on the lens. The path of the emergent rays when μ 1 > μ is :

Important Questions on Ray Optics and Optical Instruments

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The refractive index of the material of a concave lens is $μ$ . It is immersed in a medium of refractive index $μ_{1}$ . A parallel beam of light is incident on the lens. The path of the emergent rays when $μ_{1} > μ$ is :